They say he offered to sell Albany votes like shares of stock — and now federal prosecutors want to use those fundraising boasts to send state Sen. Malcolm Smith to jail.

The disgraced Queens breakaway Democrat, whose corruption trial for trying to buy his way onto the Republican line for mayor last year resumes in January, warned dozens of top New York lobbyists that their clients would be shut out of state politics if they didn’t make large contributions, the feds say in a new filing.

“Smith told the attendees that they should treat the fundraiser as an ‘IPO’ [initial public offering] by donating early while prices were low and while there was still an opportunity to participate,” Assistant US Attorney Justin Anderson wrote Wednesday of the August 2008 gathering in upstate Kingston.

“Smith’s comments implied that those who failed to make contributions to his campaign at that time would find themselves having to pay more later or being unable to accomplish anything with the Senate under Smith’s leadership.”

Smith told the lobbyists then that the Democrats were expected to win control of the Senate in that upcoming November election and that he’d be among the key pols calling the shots for the reorganized legislative body.

Linking contributions to future government actions is illegal under New York law.

Smith’s lawyer Gerald Shargel told The Post that he plans to oppose the government’s request, adding that Smith “steadfastly denies any impropriety.”

“This is clearly the government trying to manufacture evidence that does not exist,” Shargel said.

Smith told the attendees that they should treat the fundraiser as an ‘IPO’ by donating early while prices were low and while there was still an opportunity to participate.

- Assistant US Attorney Justin Anderson

The feds want to tell jurors about the fundraiser to provide context of how Smith’s history of alleged shady solicitations stretches long before he was charged in a failed $200,000 bribery scheme to cross party lines and secure the Republican nomination in the 2013 mayoral race.

Anderson said the evidence “should be admitted” to rebut Smith’s anticipated entrapment defense. Smith claims he was set up by crooked Rockland developer Moses Stern, who secretly wore a wire for the feds to dodge jail time.

The Post’s Fredric Dicker reported in 2008 that 75 lobbyists attended the Senate Democratic golf outing at the private Wiltwyck Golf Club and paid up to $75,000. During the event, Smith also referred to state Sen. Jeff Klein (D-Bronx) as his “enforcer” who would be “brutal” and “aggressive” about collecting the contributions, and said Klein “was the one managing the IPO.”

Anderson in his filing also asked Karas for permission to provide new evidence that Smith co-defendant and former Queens Vice Chairman Vincent Tabone is also allegedly a master of the quid pro quo.

The feds hope to detail at trial how Tabone, while running for the Assembly in 2010, met with Kevin E. Fullington, who was then campaign manager for Rick Lazio’s failed gubernatorial campaign.

“During their private conversation, Tabone asked Fullington to provide financial support to both the [Queens Republican Party] and Tabone’s campaign in exchange for the Queens Republican Party’s endorsement of Lazio,” Anderson wrote.